<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <title>float</title>
    <meta name="viewport" content="width=device-width, initial-scale=1">
</head>
<style>
    * {margin:0;padding:0;list-style: none;}
    ul { 
        overflow:hidden;
    } 
    li {
        width: 20%;
        border: 10px solid black;
        float:left;
        box-sizing:border-box;
        height:100px;
        padding:10px;
        }
</style>
<body>
    <ul>
        <li>1</li>
        <li>2</li>
        <li>3</li>
        <li>4</li>
        <li>6</li>
    </ul>
</body>
</html>